As part of our long-term study of phagocyte-microbe interaction we propose to further characterize and purify potent bactericidal proteins that we have isolated from the granules from rabbit and human polymorphonuclear leukocytes. We will continue to examine the almost immediate and discrete microbial envelope alterations that these proteins elicit, coincident with their bactericidal action. We will also further explore the role, in the killing and digestion of bacteria, of microbial phospholipid degradation by leukocyte and microbial phospholipases.